Heretofore, so-called "coating type" magnetic recording media, which are formed by applying iron oxide type magnetic powders dispersed in various kinds of binders onto supports, have been generally used as magnetic recording media for audio, video, computer, and the like. Requirements for such magnetic recording media, however, have become strict in view of the desire to reduce the recording wavelength and the tracking width in order to attain higher recording density. As a result, the development of "metal thin film type" magnetic recording media substantially suitable for short-wavelength recording are now in progress and have been partially put into practice.
The intention to reduce the recording wavelength and the tracking width is strict to preclude signal missing, or, in other words, drop-outs or error rate in digital use. For example, assuming an 8 mm video as a system using a tape, it is required, as a practical drop-out level, that drop-outs from -18 dB are not more than about 20 per minute. In the case of a "coating type" medium having a thick magnetic layer of the order of several microns, deficiencies or dust on the support is often hidden by the processing, such as a smoothing process due to coating, a calendering process after coating, or the like, so that signal missing can not be found. Contrarily in the case of a "metal thin film type" medium having a thin magnetic layer of the order of 0.05 to 0.5 .mu.m, not only do deficiencies on the support appear as deficiencies on the surface of the magnetic layer, but also the process, such as calendering process or the like, necessary for manufacturing a "coating type" medium, is nonexistent. Accordingly, in the case of a "metal thin film" type medium, great care must be taken to avoid missing signal characteristics.